1. Field of the Invention
This invention relates to valve and hinge assemblies suitable for use in oil and gas wells, and more particularly, to a valve assembly having a flapper type closure with a "floating" hinge. One aspect of the invention relates to a valve and hinge assembly for use in a tubing retrievable, surface controlled, subsurface safety valve. Another aspect of the invention relates to a valve and hinge assembly for use in controlling the flow of hydrocarbons and drilling fluids upwardly through a well casing whenever the drill string is tripped during drilling.
2. Description of Related Art
Flapper type closures have previously been disclosed, for example, in U.S. Pat. Nos. 1,710,410; 1,871,536; 2,162,578; 2,202,192; 2,354,310; 2,447,842; 3,672,630; 4,531,587; 4,706,933; 4,926,945; 4,977,957; and 5,044,396.
Flapper type closures With flappers that rotate from an open position to a closed position which is substantially perpendicular to the flow direction are disclosed in U.S. Pat. Nos. 2,162,578; 2,202,192; 2,354,310; 2,447,842; 4,531,587; 4,706,933; 4,926,945; and 4,977,957.
Flapper type closures with flappers that rotate from a fully open position to a fully closed position through an included angle of less than about 90 degrees are disclosed in U.S. Pat. Nos. 1,710,410; 1,871,536; 3,672,630; and 5,044,396.
A flapper type closure with a flapper having a cross-section that is a cylindrical sector and having arcuate seating and sealing surfaces generated by the line of intersection of the cylindrical sector with the wall of a cylindrical flow conduit are disclosed in U.S. Pat. No. 3,672,630.
Flapper type closures with struts that are attached to the flappers at a point spaced apart from the hinge point or hinge line are disclosed in U.S. Pat. Nos. 1,871,536; 2,202,192 and 4,706,933. U.S. Pat. No. 4,706,933 discloses a flapper valve having a control link with one end attached to the flapper and the other end attached to a spring-biased, hydraulically operated piston slidably disposed in a valve control cylinder in the valve body.
With the conventional flapper type closures previously disclosed, however, the flapper is pivotally connected at a hinge point or along a hinge line that is integrally formed as part of, or is otherwise fixed in relation to, the valve seat or body. Flapper type closures constructed in this manner experience high stress concentrations at the hinge point(s), especially when the flapper is slammed closed or is forced open against high opposing downhole fluid pressure.
Sealing difficulties are also encountered in using flapper type closures constructed in the conventional manner, especially those with contoured flappers that seal against seats extending obliquely rather than perpendicularly to the flow direction. Lap seals between the sealing and seating surfaces cannot be used because of interference that occurs in the hinge area. Elastomeric seals between the sealing and seating surfaces are therefore needed both to compensate for surface imperfections and to permit slip between interfering portions of the seating and sealing surfaces during opening and closing of the flapper.
The production of valve seats or bodies with a fixed hinge and the installation of elastomeric seals along the sealing or seating surfaces can necessitate special machining or molding procedures that increase part cost and/or undesirably reduce the load bearing area. Additionally, elastomeric seals between the sealing and seating surfaces can suffer compression failures when subjected to loading such as those encountered in downhole applications.